I need some tuning help on a OS VSPEC
 

I have a new limited edition os vspec that I have about 2 qrts on now and I am fighting a high rev before it idles down. The top end runs great but when you let off the throttle it takes about 7-10 seconds before it will idle down. I have tried everything to adjust it and nothing will work. Someone told me the carb could be defective but I wanted to get some input before I have to buy a new carb. The fuel tank is new, clutch and bearings are new, air filter was clean, and fuel lines are new. I also made sure the linkage was adjusted properly as well.

The most common thing to look at is your linkage setup bro. Also, make sure you're not binding the slide with your return spring. Eliminate mechanical issues before getting into the engine.

Engine: there are people that are much more qualified than I am, so grain of salt stuff here. I'd look at the idle gap first and then seal it up to eliminate possible air leaks before digging deeper.

Linkage or servo check. Also check your trim on the radio and maybe recenter your throttle servo.

This will eliminate that from the equation. Then you can try to adjust the engine.

The linkage is bind free and the idle gap is good. I took the motor apart and sealed it with lucky7 prior to breaking it in.

Come out on your low end and turn up the idle if you need to. Make sure your mid needle is flush and at 1:00. Every 1/8th of a turn on that mid needle can open or close it up. To see what Im talking about you could take your HSN off the carb and look down into the mid needle and turn it. Just make sure that hole is open, flush with the outside of the carb body and at 1:00. You can always do a pinch test on the fuel line about 3 inches off the fuel nipple. You should get 3-4 seconds before it revs up and dies out. If it dies out before 3-4 seconds, it's too lean. If it dies out after 3-4 seconds it's too rich. This method is just a starting point/reference.

Fatten the bottom 1-2 hrs. Pinch test. Time it takes to spool up indicates rich or lean and how much it spools up indicates your idle gap setting. If nothing changes I'd pull the needles and replace the o-rings. Definitely sounds like the carb if it was a fairly sudden change. Look at the front bearing too. If you break-in super rich it creates crazy crankcase pressure and it's really easy to force a premature air leak.

Iono...my .02 cents.

Thanks for the replies. I will definently check some more stuff out tomorrow.

Make sure there are no air leaks. And then fatten the bottom a little bit but before you do that do the pinch test and count 1 onethosand 2 onethousand Etc and see how many you count to. Should be somewhere around 4

Posted this in the OS thread as well...

Air leak!:nod: A common source for air leaks on the v-specs is at the carb pinch bolt. With the v-spec one not being o-ring sealed, there's really nothing sealing it. Anytime I've seen those symptoms on a v-spec it has been from an air leak.;)

he said prior to brak in he sealed it with lucky 7 sealent. It sounds like to me is you got in a rush on break in then went for a track tune and now its all out of wack. I would say go back to stock tune settings and start all over also what breakin procedure did u do and how many tanks of break in? NEVER RUSH BREAK IN THE MOTOR WILL NEVER RUN GOOD!

your low speed needle is too rich,maks sure your idle gap is .5-.7mm:batman:

First i want to thank you for using Lucky 7 products. second i want to tell you that if you read the instructions L7 engine sealant is intended for external use only, no dis-assembly is required. Lucky 7 sealant is a coating, not a gasket. ;)

now for your tuning. getting the perfect mixture between the LSN, MRN, and idle will eliminate any 2 stage idle on any engine. first set your idle to 1-1/4 turns in from closed, and know you dont need to touch it more then 1/8 to achieve the perfect tune. then start leaning the lsn 1 hour at a time and you should notice the 2 stage idle becoming shorter and shorter as you lean the lsn. the 2 stage idle is simply the engine loading up and burning the excess fuel in the case, now with that said if you lean the lsn too much the idle will go high and stay high, turn it back out 1 hour till its stable. < now you're close. from here make fine tuning adjustment between the LSN, MRN and idle. understanding how the needles effect each other will help you make the right adjustments so i'll give you a quick breakdown. the LSN and MRN work with each other adjusting the fuel consumption from idle to the mid rpm range, these needles should be adjusted together to achieve the optimum tune. for example if you lean the lsn 1 hour you should richen the mrn 1 hour, and vis-versa. this adjusts the fuel up or down the rpm range w/o changing the overall mixture & consumption, which will effect your idle, as well as low - mid range power. much like adjusting your idle for compensation when playing with LSN these needles effect each other. I hope this helps you have a better understanding of your idling issue.

These engines are extremely easy to tune and soo many ppl don't ever get the lsn, mrn, idle right. they easily tune the top in, lean the bottom a little and call it a day. I'll tell you what tho, if you spend the time and get the bottom dialed in you'll see the full potential of your engine and i bet you're amazed with how awesome they really are. <this goes for any brand or model.

This is why I love Rc tech!! Thank you for all the replies. I will work on it today and let you know what happens.

Check and replace your exhaust gaskets and springs as well.

If hes already cooked gadkets or somthin similar this soon then this motor shouldnt even run. He barely had 2 quarts threw it. His carb could have been put on to tight causing a tear in the seal on the inner gasket but if its been sealed then i wouldnt day that can cause to much of an issue.

Whilst the gasket on the engine could be brand new theres no guarantee the exhaust and other exhaust gasket are.

It's sounds like an air leak, and until recently i didn't realise how critical the exhaust gaskets are to a stable tune.

Check this link http://www.rctech.net/forum/nitro-of...ing-bible.html one of the first issues it discusses is carb imbalance which if you have no linkage problems it will probably help you resolve the idle issues.

oooooooooooooh yes... very often overlooked $1 item that prevents proper engine tune... I learnt it the hard way... :nod:

for now don't mind all the people telling you it's an air leak, no sense in dissassembling things when it's most likely what Joe said the LSN is just too rich and the idle gap too large. Although the only thing I would stay away from that he said is adjusting the MRN. Very few people are good enough tuners to utilize the mid range, just leave it where the factory had it (flush around 2:00). You can most likely correct your issue with just the idle screw and LSN. I would say 50% of the people at the track running nitro have a double idle of some sort, especially on Vspecs because they still get around the track just fine with a rich LSN. Some engines with a rich LSN just don't run good an force you to find an optimal tun, Vspecs will stay running even when they are way off, which is why some people love them.

Just a heads up though, if the LSN is rich enough to cause this problem, your HSN may be too lean once you get it fixed, so re-check that. If the LSN and idle adjustments don't fix it, then look possibly into gaskets, and areas that could cause a leak, sure it's possible just a lot easier to start with just one screwdriver.

Brandon,
the problem with not touching the MRN is that like you said "leave it at factory at 2 oclock" well every new engine I've seen the factory setting is different. when the carbs are manufactured they use a "power tap" to thread the carbs and the stating point is always different, so each carb is different. I usually set mine at 3-1/4 turn from bottomed (11o'clock), and it's within a couple hours of tuned. dont be afraid of the MRN, it really helps get them dialed in perfect if you understand how it works with the LSN.

check your fuel line and tank for leaks to. My mill wasn't idleing down like normal on jumps other day, found out my tank lid wouldn't seal all the way. May not be theissue, but it is easy to check and rule out.

check fuel tank, replace fuel line, check/replace pipe gaskets, return needles to factory settings and before you re tune, READ THE TUNING BIBLE.

I have too... from an air leak in the bottom of the case that cracked. Not sure if this is a problem on the new ones or not... but it is worth checking IF you don't find anything else causing it.

sounds like the low end is too lean. try getting the motor up to temp, and back low end out until it stops. Does not sound like a air leak to me, but a tuning issue. Air leak should affect the whole motor including the high end. But you said the high end runs out fine?

also try going back to the factory settings and see if it stops then

Im with Joe and Brandon. Rich LSN and too big of an idle gap. OS engines are set like this from the factory so you run plenty of fuel through them when new and they wont stall constantly but as it breaks in the idle starts to climb because its not so hard to rotate the engine.

Whats happening is the idle gap is too large so coming off the high end it stays at high idle until it starts to load up then the idle comes down.

Set the idle gap to about 0.5mm then lean the LSN out. This should get you back in the ballpark. Then make sure the HSN isnt too lean which is common when the LSN is too rich because when the LSN is rich the temps come down significantly which usually leads people to lean the HSN out too much.

With the help of all of you I have gotten the high rev down to 6 seconds before perfect idle and on the pinch test it dies at about 6 seconds. Buggy runs great now but i am going to replace the tank again just to make sure that is not causing a problem. Should the engine idle down right away or does it normally take a few seconds? I still think there is a problem some where but for now I will keep trying to fine tune.

keep leaning the lsn.. the closer you get to perfect, the shorter the 2 stage will be. you should be able to eliminate the 2 stage completely if you spend the time fine tuning as i explained.. good luck!

Can you explain what you did to bring the revs down?

Two possible conditions were:

• LSN too lean
• Idle gap too big and LSN too rich

It should idle down pretty quick in a perfect race tune. More casual or false tune settings will take longer.

Not saying you were wrong, I understand how needles work. No offense to the guy asking the question, but someone who has to ask why an engine doesn't idle down, doesn't need to be messing with a MRN. There's no reason with the factory setting that an OS carb won't achieve good idle. That's all. I ran plenty of VSpecs in my day and all of them came to idle just fine with factory settings on the mid range.

It would be like a doctor telling someone to go get a medicine decribed by all the scientific names of the ingredients, instead of saying, "go get tylenol".

Cool, I had a problem with my Losi today where it would idle high and I couldn't get it. I ended up starting over from some base settings I know are good enough to run, but not dialed in. After a few minutes it was running great again.

I find it ironic that this thread is RIGHT NEXT to the OS engine thread... (or at least it was until I posted) :lol:

:lol::lol:

I find it hilarious :ha: that some are trying to keyboard diagnose the guys problem and then arguing with each other about it when clearly the fix was in the first few postes. Bandwagon-ers on the first few postes:nod::lol:

What I find funny is when someone posts "I have a problem with my engine." There are people who jump right to "you have an airleak! take everything apart!". Most of the time it's just wrong tune. Starting over and reworking it will usually take care of it, especially if it's all new gear.

That wasn't me and I agree, you see that crapin'in all the time:lol:.. Air leaks are over rated.:tire:

what would blow me away is to fix an engine problem on a chat forum! :lol:

Actually adjusting the mid range with the lsn and idle helped. I may be new to nitro but I can work on anything and understand mechanics very well. I like to ask questions when something is new instead of just assuming something and then blowing up a new engine. All the suggestions have helped and I hope after tomorrow it will be all good. Thanks for everyones help.

Hey in the end regardless of what anyone says this is a hobby. Hobbies are meant to be fun and enjoyable. As long as you enjoy R/C then all is good.

pitpop I understand what you're saying, but there are some very common mistakes that people make with Nitro engines. These mistakes have easily recognizable results (high idle, won't idle, bog at wot, bog at low throttle etc). Those problems can be diagnosed through trial and error and someone who doesn't know what causes a particular condition, would do well to ask for advice on things to try. If it doesn't work you can always turn the needle back to where you had it and try something else.

The biggest thing that I have learned with nitro so far is how small adjustments can make a real difference in tune. I printed off the tuning bible as well as all of your post and it helped alot. Thanks again to all who have posted.